, I figured out how to use Google Analytics (GA) to filter for mobile devices, i.e. filter for visitors to your Analytics-enabled site who are coming to it from a mobile device (such as an Android, iPhone or iPad):

Go to left pane of GA -> Visitors -> Mobile -> Mobile Devices

That's it. It will show you statistics on mobile device-using visitors, with the break up by type of device such as Android, iPhone, etc.